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Photo of Thomas Coyne, proprietor of his eponymous winery in Livermore. He is a chemical engineer who worked at Clorox. This is for a story on acid testing in wine. Photo of Thomas Coyne with a SO 2 Aspirator (the 2 needs to be lower case), which measure the free sulfur dioxide in wine. That is rose wine he is testing.
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Photo of Thomas Coyne, proprietor of his eponymous winery in Livermore. He is a chemical engineer who worked at Clorox. This is for a story on acid testing in wine. Photo of Thomas Coyne with ... more

Photo: Craig Lee

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Photo of red wine. Photo to go with cover story on the impact of San Francisco food on the rest of the country. Food styled by Amanda Gold.
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Photo of red wine. Photo to go with cover story on the impact of San Francisco food on the rest of the country. Food styled by Amanda Gold.
Event on 8/25/05 in San Francisco. Craig Lee / ... more

You might think OJ, because of its citric acid. Yet Pepsi is more than 10 times as acidic, according to figures provided by PepsiCo, which makes both.

Why am I writing about Pepsi in the Wine section?

Because acidity may be the least appreciated quality of a wine's flavor. Crisp acidity in wine is delicious and refreshing -- just as it is in Pepsi -- but even many frequent wine drinkers think it's a bad thing.

Acidity is what keeps wine safe from microbes and helps it endure and improve over years in the cellar. It even makes wine smell better.

"When you move the pH (a measure of acidity) down to a more acceptable range, the bouquet changes," says chemical engineer and winemaker Thomas Coyne. "The aroma just seems to blossom."

But there's something about that word "acidity" that summons negative images. At best, it's Timothy Leary, and the Electric Kool-Aid Acid Test. At worst, it's sulfuric acid, battery acid, stomach acid, maybe even Phantom of the Opera. In fact, the first definition of acid in Merriam-Webster's Collegiate Dictionary is "sour, sharp, or biting to the taste."

Last year, Wine Opinions of St. Helena surveyed frequent wine consumers about which descriptive terms found on Cabernet Sauvignon wine bottles appealed to them.

Some reactions were different by gender: More women were attracted to "jammy fruit," while more men wanted "heavy and full-bodied" wines.

But a plurality of men and women, young and old, agreed that they don't want wines described as "crisp or tangy with distinct acidity."

"Only 'dry and tannic' came out worse," says John Gillespie, founder of Wine Opinions.

Whoa. "Crisp acidity" is a phrase most wine writers, myself included, use as praise, particularly for white wines.

But, Guffy says, "Acidity for the consumer just boils down to tart or not tart."

Yet tartness and acidity are not the same. Like Pepsi, wines such as German Riesling can be tremendously acidic and not taste tart at all. Maybe wine professionals need to explain this better.

So here goes.

Crisp acidity is the taste of lemonade on a hot day. It's the salsa in a meat-and-cheese burrito. And yes, it's the main reason we think Pepsi tastes great with pizza before we're old enough to buy Sangiovese.

"Lower-acidity wines have a flaccid mouthfeel. They're just flabby," says Coyne, who owns Thomas Coyne Winery in Livermore. "If you get too high, they've got a bitey tongue-feel. There's a range you need to hit."

When I was a tyke, at the fringes of my memory, I drank milk with my food -- burgers, hot dogs, even vegetables.

Milk is almost neutral, with a pH of about 6.6 on a scale of 0 to 14, according to the U.S. Food and Drug Administration. A pH of 7.0 (water or soybean milk) is neutral; lower numbers are more acidic, higher numbers are more alkaline. Most wine is between 3.1 and 3.8, roughly the same range as applesauce and strawberries.

When I was deemed old enough to choose, I preferred soda with my meals. Sure, I liked the sugary sweetness and the fizz of carbonation, but even at that age, I also liked the way it cleansed my palate. Milk felt flabby in my mouth. It wouldn't wash out the flavor of pork chops, much less (ugh) asparagus.

"Soft drinks are very acidic. When I was a child, I remember my parents using Coke to clean out a radiator," says Hildegarde Heymann, a sensory scientist and professor of viticulture and enology at UC Davis.

Coca-Cola Classic is about the same pH -- 2.5 -- as Pepsi, according to Heymann. (The Coca-Cola Co. did not respond to requests for data.) They are both far more acidic than some things we think of as tart, including grapefruit juice and cider vinegar.

So why don't Coke and Pepsi taste tart? Because they also include a pile of sugar, which doesn't affect the actual acidity, but makes a huge difference in how we perceive it.

"More sugar will make it taste less acid," Heymann says.

The converse is also true: A completely dry wine allows you to taste its crisp acidity in a way that, for example, a white Zinfandel with residual sugar -- sugar that is left in the wine, rather than converted to alcohol -- does not.

"One of the things that makes white wine such a nice food wine is it cleanses your palate," says the Hess Collection's Guffy. "It's not as refreshing to have something sweet or flabby."

In fact, I would not describe Pepsi as having "crisp acidity," though it is far more acidic than the Sauvignon Blancs I now prefer with my meals. Not to knock Pepsi, but for wine drinkers, weaning oneself from the taste of sugar is part of growing up.

Perceived acidity is complicated; it's hard to tell just by tasting how acidic something actually is (See "Acid Eaters," Page F5). Sugar is not the only thing that can affect how acidic something tastes. The types of acid present and the form they're in are even more important.

Moreover, pH is not the only measure of acidity.

Measuring acidity

Wineries measure acidity two ways: total (or titratable) acidity and pH. Both are a measure of hydrogen ions -- these are what make an acid an acid -- but they measure them in different forms. Anyone who passed high-school chemistry is familiar with pH, but for wine, total acidity -- which includes all hydrogen ions, even from acids that are dissolved into other compounds -- may be more important to consumers because it affects the flavor more.

"An acid is by definition a substance that releases hydrogen ions into a water solution," says Palo Alto-based food scientist Harold McGee. "What our taste buds detect for the most part is hydrogen ions."

McGee points out that acidic foods and drinks are -- literally -- mouthwatering.

"Acidity stimulates salivation," says McGee. "It's a protective mechanism on the part of the mouth. Your mouth tastes something acidic and wants to neutralize it. Saliva is alkaline."

PH does not measure acids that have bonded with other compounds to create salts such as potassium tartrate. The glass-like crystals that you sometimes see attached to the inside of wine bottle corks are potassium tartrate. They're edible and harmless.

PH matters in winemaking because free-floating acids in wine kill unwanted microbes. If the pH drifts above 4.0, it's an open invitation for foul-smelling bacteria to breed.

"It wasn't until (Louis) Pasteur that we knew how wine was made. Prior to that, it was like magic," Heymann says. "In low-acid situations, you'd stick your nose in it and it would be disgusting."

Numbers don't show flavor

But the perception of acidity doesn't follow the numbers for either total acidity or pH. I learned that at a recent production tasting at Silverado Vineyards in Napa, where winemaker Jonathan Emmerich was considering what to do with several barrel samples of Carneros Chardonnay.

More than any other grape, Chardonnay is the harbinger of a nation's taste for acidity, because Chardonnay is arguably the most manipulable of wines. Chardonnays can range from the minerally, crisply acidic wines of France's Chablis region to mouthfilling buttery California wines.

The latter have been popular in the United States for years, but The Chronicle tasting panel's recent tasting of Napa Valley Chardonnays revealed that the pendulum may be swinging toward more balance and more distinctive acidity. (See Page F6) Wineries say this shows the impact of restaurant sommeliers who appreciate the food-matching qualities of wines with crisper acidity.

Emmerich printed out a chart of the total acidity and pH of each sample for the Chardonnay tasting. His purpose was to decide whether to issue a new single-vineyard Chardonnay from recently planted vines whose grapes yield a distinctive olive-like flavor, or to blend that wine as a spicy element into a Carneros region bottling.

The acidity numbers appeared to play no role in his decision-making process; we talked about the aromas and flavors of the wines for hours, but never really discussed the statistics. But I was already working on this article, so the numbers were fascinating to me for their lack of predictive value.

The most tart-tasting sample of the day had only the third-highest total acidity; moreover, its pH was a higher number (indicating less acidity) than all but two other wines.

The sample in which Emmerich was most interested -- an unoaked wine from the new vineyard in Vineburg in the portion of the Carneros region in Sonoma County -- had far lower total acidity than almost everything else we tasted, and its pH number was the second-highest. Yet my tasting notes include "lemon-lime and lemongrass," and I liked it well enough that I might have anointed it with that consumer-unfriendly sobriquet crisp acidity.

Weather plays a role

Emmerich told me the wine didn't start out this way.

"(Last year) was an incredibly long year," Emmerich says, adding that the long, cool growing season led to acidity in some wines that he called "shrill." But he was able to turn down the acidity's volume, if you will, through malolactic fermentation.

Malolactic fermentation plays a huge role in the perceived acidity of wine. The tart-tasting malic acid that naturally occurs in wine grapes is converted by acid-loving bacteria into softer lactic acid -- the same acid found naturally in milk products. If you smell and taste butter in your Chardonnay, that's the product of malolactic fermentation (malo for short).

Malolactic fermentation can occur naturally, it can be prevented, or winemakers can inoculate their nascent wine with lactic-acid bacteria to make sure it happens in the winery and not in the bottle after it's sold.

"It's all about balance," says Emmerich. "We don't want too much butter, but malo does make the wine more complex."

The other main type of acid found in wine grapes, tartaric acid, is also easily manipulated by winemakers, simply by adding or subtracting potassium tartrate.

"I'm perfectly willing to adjust acidity as needed to make it so that it feels right to me," says Merryvale Vineyards winemaker Steve Test. "It's like adding salt to the soup. You do it until it tastes right."

Chardonnay, along with Cabernet Sauvignon and Merlot, is easy to work with because its natural acidity tends to be balanced, Coyne says.

Syrah and Zinfandel often don't have as much acidity as required. This is ever-more true because winemakers are encouraging grapegrowers to leave their grapes on the vine as long as possible so the fruit gets ultraripe. The longer the grapes ripen, the more the hydrogen ions are absorbed into imperceptibility.

On the other hand, some grapes -- notably Grenache, Barbera and Sangiovese -- are blessed with high levels of natural acidity.

"I've been getting Grenache and Syrah from the same vineyard," Coyne says. "Grenache comes in with low pH and nice acid. The Syrah from 100 yards away will have high pH and need acid."

The age factor

Acidity is the key to a wine's age-worthiness. This is why Rieslings from chilly Germany can age far longer than most white wines, and why some wines from France are expected to taste fresh after decades. It's also a reason that many people wonder if classic-style California wines, with lower natural acidity than those of Europe, will age well.

"I've heard a lot of people wonder how long high-pH wines can last," says UC Davis Professor of Viticulture and Enology Andy Waterhouse. "The lower the pH, the longer-lasting the wine will be."

Let's review: Crisp acidity makes wine smell better, taste better and last longer. It will cleanse the palate during meals and protect wine from microbes.

In short, it's a good thing. So when you hear "acid," don't think about burns, blisters and excessive '60s rock. Think peaches, apples and raspberries. Or best of all, think of a delicious Chardonnay, Merlot or Cabernet Sauvignon, and thank your lucky hydrogen ions.

"Make up some sugar water," says Heymann. "Ten percent sugar is about what Kool-Aid is. Taste it. See how much you like it. Then add some lemon juice and do the same thing."

I tried it. The sugar water was boring and unappetizing. Moreover, it didn't taste anywhere near as sweet as the same sugar water with lemon added. That's a major reason why Pepsi and Coke are so acidic -- so they can deliver more sweetness.

"When you make lemonade, you add lemon not just for the flavor," Heymann says. "Even Kool-Aid has acid."

So consider this the non-electric Kool-Aid acidity test.

-- W. Blake Gray

Acid eaters

Here are the approximate pH levels of various foods and drinks, according to data from the U.S. Food and Drug Administration. A pH of 7.0 on a scale of 0 to 14 is neutral; lower numbers mean more acidity, and higher numbers are more alkaline. The scale is logarithmic, so that basil pesto, at 4.90, is 10 times as acidic as cheddar cheese; red Delicious apples, at 3.90, are 100 times as acidic as cheddar.

2.0 -- 3.0

Lime juice 2.00 - 2.35

Lemon juice 2.00 - 2.60

Cranberry juice, canned 2.30 - 2.52

Grenadine syrup 2.31

Pepsi 2.5

Diet Pepsi 3.0

3.0 -- 4.0

Wine (about 3.1 -- 3.8)

Raspberries 3.22 - 3.95

Peaches 3.30 - 4.05

Apples 3.33 - 3.90

Ketchup 3.89 - 3.92

Dole orange juice 3.9

4.0 -- 5.0

Cherries, California 4.01 - 4.54

Cream cheese 4.10 - 4.79

Tomatoes 4.30 - 4.90

Pickled herring 4.50 - 5.00

Basil pesto 4.90

5.0 -- 6.0

Bananas (yellow) 5.00 - 5.29

Green peppers 5.20 - 5.93

Whole wheat bread 5.47 - 5.85

Garlic 5.80

Cheddar cheese 5.90

6.0 -- 7.0

Black olives 6.00 - 7.00

Egg yolks 6.10

Avocados 6.27 - 6.58

Peanut butter 6.28

Milk 6.40 - 6.80

7.0 -- 8.0

Soybean milk 7.0

Water 7.0

Lobster, cooked 7.10 - 7.43

Graham crackers 7.10 - 7.92

Camembert cheese 7.44

Egg whites 7.96

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